Monday, September 28, 2020

Building a new lithium battery

For years I have been using lithium batteries to power my radio equipment when portable, both LiPo and LiFePO4.
If you want to know more about these different types read this post I wrote a few years ago.

I started out buying batteries from HobbyKing in China. Then I decided to build a few myself with pouch cells I bought from AliExpress. 

Recently I lost two LiPo pouch cells when I abused a battery - forgetting to attach the under voltage alarm. Another LiPo cell of a different pack turned out dead without a clear cause. I ordered a new cell but they are quite expensive. Losing three of those cells in a short period of time I suspect I might have to replace more in the future. So I started looking for other solutions with cheaper building blocks: smaller cells.

LiPo cell after abuse

Looking at smaller cells I first stumbled upon the 18650. A popular Li-Ion battery and quite small but you need a lot of them to get a useful capacity as they are around 2Ah a piece. However I found more practical LiFePO4 cells with a 7Ah capacity: 32700. I bought a set of those with strips of nickel attached to the ends for soldering as I do not have a spot welder (yet).

The voltage of four of these LiFePO4 cells is too low for my amp - that is why I opted for LiPo up till now - but as the amp is designed to handle up to 18V a battery of 5 cells would do the job. So I decided to go for a 5s3p design (5 cells in series and 3 in parallel).

Building a 5s3p battery

I bought a BMS as well with the idea that it will protect the battery from under voltage. And it allows me to charge the battery even with a simple (non balancing) charger. I was hoping that a BMS is more effective in balancing than the chargers I have - that take quite some time to balance an unbalanced pack.

Completed battery with BMS

Testing the battery my first lesson was that you cannot charge a battery that has a BMS with a smart charger. The BMS starts kicking in when the first cell approaches its maximum. The charger notices the increasing resistance and shuts down with an error ("connection break"). 

Charging through the BMS with a smart charger 

Time for Plan B I used a 12V source and a step up converter to 18V to act as a "dumb" charger. Meanwhile I checked the charging current and the voltage of the individual cells to see what was happening. 

This time the charger patiently waited for the BMS to allow for a current to run. The BMS would drain the cells for a bit and then allow a charge current until one of the cells hit around 3.5V and then the cycle repeated. However it did not seem to be able to bring the cells closer together. After an hour there was still a spread of 0.2V between the cells. 

After letting the pack sit for a while I found out that the BMS aims to keep the cells at around 3.4V (on my V-meter). So during charging - aiming for 3.6V - a cell might go higher but the BMS will continue to discharge it until it is back at 3.4V again.

I will have to see if this noticeably impacts the capacity of this battery pack. When I have some more time on my hands I will run some tests and see how it behaves under the stress of powering a 400w amp.

Update May 2021:
After using the battery pack for a while I decided to remove the BMS. In my situation - having balancing chargers - the BMS only adds complexity.

The second thing I noticed is that the pack was struggling delivering the high amperage the ALS-500m pulls. Testing the pack at home with a dummy load I saw the nickel tabs I used to solder the main + and - wires to became hot, red hot even. 

So I decided to solder wires to the first and last set of (three) parallel batteries to spread the current. Testing that thoroughly I found it to work perfectly. All cells now discharge evenly, even under high load.

Shrink wrapped end result (with built-in Voltmeter)

Friday, August 7, 2020

40m wire antennas compared

Before going on holiday I managed to get some life into my old C-Pole using a new home made choke. I re-tuned the antenna (with some challenges) but did not get a chance to use it. 

In the past I did use it quite a bit and was pleased with the results but as always - this does not tell you a lot. HF conditions vary too quickly and dramatically to base any evaluation on single antenna experiences. You really need simultaneous A/B testing.

A gap in my schedule allowed me to go out and do some testing of different wire antennas for 40m. I ended up testing a C-Pole versus an end fed halve wave more or less vertical and the same C-Pole versus an inverted V dipole.

Test setup

I used two identical WSPRLite beacons that transmit with 200mW on the WSPR frequency. 

  • The C-Pole was set up so that the feedpoint was at approx 2m above ground (that would be your typical setup with a 12m pole, like the Spiderbeam I have - with the top of the antenna at 11m). 
  • The EFHW was attached to my 18m pole and therefore almost vertical. The last 3-4m I set up sloping so that the feedpoint was at approx 1.5m above ground.
  • The Inverted V was set up so that the feedpoint/apex was about 13m high. 

The test period was the end of the afternoon. Not the best time for 40m and certainly not the best time to test DX performance. However it was the time I had available. 

C-Pole meets EFHW vertical

The first run was the C Pole vs the EFHW vertical. I let the beacons run for about an hour. After that time I had:


On first glance the EFHW vertical seems to fare better. It has been heard more often. However both antennas reached the same amount of spotters. So nothing too dramatic here. There is not a lot of difference in the stations that received the signals - so most of the spotters returned data for both antennas.

Now looking at the SNR reported by the spotters there is more to say about the difference. I averaged the reports per spotter to decrease the amount of data points. The graph below shows the signal strength reported (SNR in dB on the Y axis) at the spotters' distance. It looks like the EFHW (in orange) performs better.

I then calculated the average difference in signal strength per spotter of the EFHW over the C-Pole - so only for spotters that returned reports for both antennas. The graph shows the difference the EFHW scored in dB - above the line means the EFHW beat the C-Pole. 

This clearly shows the EFHW beats the C-Pole on almost all distances and sometimes by a fair margin. The outlier is S51RS at 950km. That is the only spotter favoring the C-Pole significantly.

So if you have enough height available the EFHW is the one to choose out of the two at least for the ranges tested today. This is what I expected from the theoretical analysis I did some time ago.

An interesting followup would be to see how the EFHW would perform with the same top height (sloping from the 12m pole or tree branch). With a slingshot one can easily get a vertical wire up 20m, so I would normally aim for that height with this antenna.

C Pole meets inverted V dipole

Now how about the inverted V? This one adds another element to the game as it is horizontally polarised (as opposed to the vertical EFHW and the C-Pole).

I chose a height around 13m (not fully extending the 18m pole). In retrospect I might as well have gone 2 meters lower to compare the antenna if set up on the same 12m pole as I used for the C Pole antenna. Here we have a slight advantage for the inverted V.

Running the beacons for just under an hour I had:

Inverted V1146219

The inverted V got one extra shot so it is hard to tell from this first glance which one performed better. 

Looking at the average report per spotter shows that the Inverted V (in green) seems to beat the C-Pole on most occasions. 

Moving one step further the indication is confirmed. The Inverted V wins (above the line) almost everywhere. The biggest outlier again is S51RS.


I did not test the inverted V against the EFHW vertical directly. However looking at the differences per test, using the C-Pole as "a reference antenna", there does not seem to be a lot of performance difference within EU. I would have expected the inverted V to do slightly better than the vertical on the shorter distances (with its higher radiation angle) but that might be only noticeable on even shorter distances.

So, this time I learned that within EU the C-Pole loses against an inverted V at more or less the some top height and loses against a vertical EFHW with the feedpoint at more or less the same height. 

One question remains - as the antenna's have different radiation patterns - would any of these clearly beat the others on multi hop DX? The simulations I did previously would suggest that the C-Pole would have an advantage over the inverted V because of more low angle radiation.

If it turns out the C-Pole does not "deliver on promise" there, then I cannot see a lot of situations where I would choose it over one of the other designs. Only if the footprint needs to be minimal and height is restricted (*).

This last question requires a new test around gray line time - when I can't use my favourite test ground as it is only accessible in daylight. Something to put on the "to do list".

*) Another one: would the C-Pole beat a shortened 40m EFHW of equal height - so approx. 12m? I have such a wire with spool that I used in the past for my 10-20-40m EFHW.

Wednesday, June 3, 2020

FREE month

Last month I spent more time on the radio than the preceding twelve months combined. I was on the air as one of ten stations with a special call in the P*75FREE(DOM) range to commemorate the end of WW2 in The Netherlands in May 1945.

Planning the event at the end of last year we had ideas to be active as a group or subgroup during the month with a large event from a war museum. They were happy to accommodate us a whole weekend. However COVID-19 changed all that. 

Initially I went out /P alone to a couple of PAFF nature reserves but as the month progressed we decided to do a smaller group activity with three operators from a nature reserve (PAFF-0168). We were able to set up two stations - one 40m and one 10 to 20m using the portable hexbeam. We changed the latter into a 60-80m station in the evening.

Hexbeam set up in a nature reserve with PD75FREE, PG75FREE and PH75FREE running two stations

Through email and Telegram chat the FREE stations kept in touch on the progress, the conditions and notable experiences. It is nice to see how working as a team motivates one to be more involved and spend more time behind the radio. Each participant made different choices based on preferences (like more or less digi) and set-up.

Another motivating factor were the most active chasers that tried to find us on each band and mode and even contacted us by email or Facebook to share their enthusiasm and look for opportunities to work us with OH2YV as the most striking example. His dedication was extraordinary. He finished first by a stretch only using phone and CW (so missing all possible digi points most other chasers did collect). 

All in all we made 25.000 QSOs with 13.000 stations. I was not the most active by a long stretch but still made a nice amount of contacts spread over the bands and modes (giving serious chasers a chance to accumulate points). There was a nice bit of sporadic E in the second half of the month, allowing for short skip on 20 and 40 but also openings on higher bands up to 2m.

In three pictures an idea of my activities (star = digi, dot = phone/cw):
VHF and high HF: 2/4/6/10/12/15m - sporadic E fun within EU

17/20m gave both Es and some F2 DX

Low band (30/40/60/80/160m) throughout EU and one DX on 40m to PY
To be able to work the chasers on low bands and further than the first hop (DX was challenging), I went out one last time in the last weekend of our activity to a piece of wasteland where I could set up an antenna for 160m. PD7YY joined me to see if we could work DX on 40m as well - and we did with PP7DX making it all the way.  

18m pole with low band wire antenna's and our YNOMY flag

After finishing collecting all data and producing 400+ awards the following challenge is QSL-ing all our chasers. For now the radio will enjoy some rest - probably until I go on holiday. I hope to be able to go camping in France - like previous years. We'll see how things progress in this peculiar period.

Wednesday, April 29, 2020

C-pole tuning part 3

This weekend I went out to test my C-pole with a new 1:1 balun. As I blogged before I ran into trouble with this antenna and the common mode choke I constructed in W2DU style.

To rule out any balun influences I had decided to tune the C-pole last week using my VNA without any balun present. My idea at the time was that this would give me the most clean picture of the antenna and would rule out any failure of the balun ruining the tuning process. Smart move? No. (but I learned something).

While working on the "naked" antenna I was amazed how much off it was. To me at the time it seemed strange (I tuned it before didn't I?) but it did explain why it failed in operation. So I continued re-tuning the antenna - moving the feedpoint a considerable bit along the one leg of the folded dipole (basically the C-pole is a dipole with the ends folded in a square shape towards each other).

After 1,5-2h of pushing the antenna up and down again I had a perfect match in the 40m band. One happy camper.

At home I tested and optimised my 40m balun. Ready for the final assembly and testing.

This weekend I had some time to go out to bring it all together and enjoy the fruits of my labour. However when I set up the antenna with balun I found.... it was way off. Go figure.

Tuning the C-pole yet another time

Discussing this with my YNOMY team members we came to the conclusion that the common mode current - considerable in this design - influences the measurements of the VNA. So tuning the "naked" antenna was a stupid idea and the time spent tuning was actually time spent detuning it.

A frustrated ham is never going to be the best person to work on any project but I did decide there and then to re-tune the antenna one more time. I was almost finished when I too hastily bumped the VNA against the pole. The center conductor of the SMA plug attached to the VNA broke off and is now securely in place in my VNA port - making it neither a female nor male connector (gender neutral - a modern concept). That concluded the tuning process for the time being.  

Gender neutral SMA connector

So now I have to replace the SMA connector on the VNA. That connector - I found - is soldered into place with lead free solder that I cannot remove with my soldering iron as it just does not heat up enough.
Luckily Marcel PG8M told me he both has the connectors and a proper soldering iron. So now I have to find the time to go over to his place and have him repair the damages (keeping a safe distance all the time of course).

Saturday, April 18, 2020

Cooking on a choke

Out portable with my (relatively) new C-pole antenna last week I ran into trouble. After about 30 minutes signal levels dropped dramatically indicating something was wrong. I saw the SWR skyrocket.
Walking over to my c-pole I felt the common mode choke was boiling hot. So I changed antennas and continued my operation.

Back home I began my investigation in what went wrong. Immediately there were two suspects: the antenna (high swr for some reason) and the choke (too low choking impedance).

The antenna was fine when I used it the first time and I did not change anything in the mean time. So the choke seemed a more logical candidate. The purpose of the choke is to minimise the amount of common mode current that you will generate with an unbalanced antenna like the C-pole. If the choking impedance is too low however there will still be a considerable common mode current left that will generate heat in the choke.

W2DU style choke with ferroxcubes beads
On this latest homemade version of the c-pole I use a W2DU style choke that I constructed myself using a number of ferrite beads. The type and amount I used I based on the factsheet. On paper the choking impedance was OK but I can't remember if I really tested it. Checking it now I measured a whooping 400 Ohm of impedance - far too low to stop the CM current flow (I wonder if the heat impacted the ferrite?).

Removing turns of RG58 from two stacked FT240 toroids

On my first C-pole I used a different current choke, designed on the basis of the excellent information by the late G3TXQ. I used two FT240-43 ferrite toroids stacked with a couple of turns of RG58. It is bulkier and heaver though than a W2DU choke, that is why I changed it.
That toroid based choke also became very hot on my first c-pole but I later discovered the antenna itself had an issue - causing high swr - causing high voltages over the choke.

So I returned to this old choke - abandoned but not scrapped. I measured it and it had an interesting profile. It was particularly useful in the 80m band range (5k Ohm) but certainly not bad in the 40m range (2.5k Ohm).

Measurement #1 of the choking impedance and transmission loss on my balun

I decided to take it apart and remove one of the RG58 turns. As expected the choking maximum moved up. The profile now suited a 60m antenna perfectly while impedance was higher in the 40m band. After removing two more turns I got a maximum in the 40m band. The choking impedance is now more than 5k Ohm there. That should do the trick.

Measurement #2 after removing 3 turns of the coax

When I have the time I will go out /P with my C-pole to check it without a choke - just to be sure it still is resonant in the 40m band - and then add my old toroid based choke. 

Tuesday, April 14, 2020

Recent PAFF activities

Covid-19 has motivated me to go out portable again after months of little to no activity. Apart from some field tests I went out for two PAFF activations. One to PAFF-0016 (Sallandse Heuvelrug) that I visited once before in 2012 and one to PAFF-0055 (Deelerwoud) that I had visited four times already as it is near to my QTH.

The PAFF-0016 activity was on the Saturday afternoon during WPX SSB. There was no choice in the matter as I was out with my family and there was only that particular afternoon available. I was doubtful about my chances to work a nice number of stations (my target is a minimum of 100), but it was even worse than I feared. In 2,5 hours I only logged 26 QSOs from 13 DXCC. That is by far the lowest number I have logged during a WWFF activity.

It started out alright with K2VV (Missouri) as the first chaser coming back on 20m but then the contest QRM became stronger and stronger. The higher bands were closed (4 QSOs on 17m in 30 minutes), so I tried some (fake) CW on 20m. That gave me a few new chasers but that was slow with 10 chasers in 30 minutes. In the end I went down to 60m to add another 7 QSOs before calling it a day.

QSOs from PAFF-0016 - nicely spread out but only a handful

My visit to PAFF-0055 was the next Saturday and was completely the opposite. There was a contest that weekend but it would only start at 16h UTC. That gave me some time to use 20m and 40m before QRM started. 
The 6th chaser to return my call was Norm N9MM from Texas. That was good propagation news as TX is not regularly in my /P logs. Two more DX surprises were a new JA chaser and Paul VK5PAS who I had not heard for 3 years. 
Europe was well awake and the skip zones of 20m and 40m overlapped nicely. It was busy throughout. I logged 156 QSOs from 32 DXCC in just under 2 hours even though I had to change antennas for 40m as I seemed to have burnt the common mode choke of my C-pole...

QSOs from PAFF-0055 - activity level that makes an activator smile
That last activity was motivating which is good because I have a busy month of May ahead. I will be active with a special call - PH75FREE - commemorating 75 years of freedom (after the end of WW2). I hope to do most of the activity /P.

Sunday, April 12, 2020

Up a tree - part 2

After dusting off my EZ-hang slinghsot I replaced the old and in the meantime shortened fishing line with new fluorescent line (0.25mm). I started out with 120m but that was a little too much for the reel so I cut it back to 100m.

I was wondering what the effect of the different sinker weights would be in practice - which one would travel higher and how would they behave once up in a tree.

Slingshot with 1.75oz sinker
Slingshot with original sinker

First I did some simple shots across a field. It turned out both weights ended up at around the same distance: 50m (170ft) with a maximum of 54m for the 1.75 oz weight and 58m for the original 1oz weight. I would say comparable.

Lots of nice branches
Then I selected a few nice trees to compare the two sinkers further. Again the difference in height reached was not really significant. Both ended up around 25m (80ft) with the 1oz weight reaching the highest branch at 28m (90ft). This corresponds to the highest mast I have (26m) so more than acceptable.

Two differences were significant to me:

1. the original (yellow) sinker was easier to find (higher visibility thanks to the paint)
2. the heavier sinker came down smoothly every time while the original one had to be helped down more than once (tugging the line)

So I think it is a matter of painting the heavier sinkers and I am good to go.

Another thing I will optimise are the rubber bands of the slingshot. They can be stretched quite lightly even up to my maximum reach. As it turns out (as with everything you dive into) there is a whole unknown territory to explore when it comes to designing good slingshots. Another thing to put on the to-do-list. On top of that list is figuring out why my 40m c-pole antenna kills current chokes. More on that later...

The "chosen one" in action

Friday, April 3, 2020

Up a tree

Being confined to home during the whole week - working remote through video links - I was looking for an outdoor activity. I decided to do some testing on my various options of launching wire antennas in a tree. Being able to deploy an antenna at a decent height without a mast increases the options for effective activities /P. 
In my little test this Sunday I used two different weights and my slingshot (by EZ Hang).

When I started looking for ways to get a wire up a tree I tried various objects and lines. I found out quickly that it is important that the wire is smooth - so fishing line or decoration line (used in shop windows for example) is the way to go.

Decoration and fishing line

As to the object to throw you need something that is easy to handle, smooth / round (so it glides through the branches) and a convenient throwing weight. Regarding the weight you are looking for a sweet spot: heavier and it will get difficult to throw high, lighter and the object will not return your line back to earth but just keep on dangling somewhere high up in the tree. In that situation you are left with tugging the line hoping the object continues its descent but in my experience you might just as well cause the object to swing around the nearest branch - leaving it behind for eternity. 

I started out with a ball as throwing object. Trying different types I settled on a field hockey ball. The reason being that it fits my hand perfectly and the weight is around the sweet spot (150gr) - not too heavy but generally enough to bring the line back down. Just drill a hole through the middle and away you go.

The ball is kind of large though so not so practical to carry around. Later on I started using fishing sinkers, settling on the heaviest one I could find (90gr). 

Throwing weights: hockey ball and fishing sinker

I tried both and measured the height I could get a line up. Of course it is slightly unscientific as I used only one tree in this experiment - so not all heights were achievable only specific branch heights. It turns out I can throw the fishing weight just a bit higher than the ball. A few tries brought it up to 12 meters / 40 feet. A decent height for a wire antenna on the higher bands.

EZ Hang slingshot

Then I turned to my slingshot. I have been struggling with it in the past, getting the line stuck in the reel or not having the ball come down from the tree (losing a lot of line).

After a few tries I did manage to shoot the provided metal ball a nice way up and through the tree reaching a height of 25m. I think I can shoot it higher than that if I give it a bit more practice. That is a good height even for wire antennas on the lower bands.

The EZ hang standard weight - a 25gr canon ball

The main weakness to me is that the weight of the standard ball is too low to be sure it comes down from a tree with a lot of branches (let alone leaves). So the next thing I will do is test this out with a few different weights. I also have to replace the line as it has become too short after losing parts of it in the past (stuck in trees).

Will share more experiences in the future.

Wednesday, March 18, 2020

Crazy things that happen when you are a portable ham

Beware it has become a long post..

When I am out working portable I look for places where I am not in anyone's face. That is easier with a wire up a tree and more challenging when using my portable hexbeam. It usually means I am in a desolate place. Either in a nature reserve (as WWFF activator) or some other park or abandoned space to test antennas or work specific DX.

Being out there as ham radio operator for some ten years now I have had a couple of memorable encounters. I thought it would be nice to share some.

Meeting police

More than once I have met police while being out working portable. Not surprisingly the officers generally want to know what I am doing. Most of the time they are curious but move on when they find out I am rather harmless. Once in a while the officer is old enough to remember the time a lot of people had (CB) radio's so chats a bit longer. Like any other passerby the comments on the hexbeam are usually along the lines of "hanging out the laundry?".

In my village I had a meeting with police one time when I was driving home after a low band activity in the early hours of Sunday morning. The patrol car stopped me as they probably had nothing else to do and I was the only one driving around at the time. The funny thing is that the first officer was somewhat suspicious of the amount of stuff in my car (radio gear, antennas, wires, Spiderbeam poles and my aluminum mast). She kept asking me questions to figure out what she was dealing with. But then her partner came up to the car and said "he is a radio amateur" (that it explains it all, right?).
The crazy thing of course is... how did he know? Clearly one of the earlier encounters had lead to a note in the police database. I am now formally known as the odd ham radio guy.

There was one police officer in PA that was more than annoyed with my activity. It was during an activity close to the coast. She did not understand what I was doing and kept on repeating the she found the whole thing fishy. However she also concluded (implicitly) that there were no grounds to stop me, so in the end she moved on - but visibly reluctantly.

The most depressing encounter was a meeting with the honorary police in GJ. They were ignorant of ham radio but did not let that fact keep them from acting tough. They drove up to our lovely desolate place where we had just set up the hexbeam (see below) and a low band inverted V. Unfamiliar with what we were doing - as foreigners, at dusk - they were determined to put an end to all of it. However, they had no real arguments that we could no counter (like: "you will be influencing the air traffic communications"). It was late Saturday evening and dispatch was not going to give them any guidance. In the end they settled on the need for an air traffic supervisor to give us permission. Of course that person would only be available the next morning. So we lost one park activity that day. (the air traffic supervisor laughed the whole thing off by the way)
Hexbeam ready to push up in GJ - just before the honorary police turned up

Meeting park management

So far my experiences with park management - that you are likely to meet when you are a WWFF activator - are nothing but positive. In fact most of the time they ignore me. Of course I take care not to damage anything or be in anyone's way.
Once a ranger approached me and asked if I was working for the national broadcasting service. That was a first for me. It turned out he was actually having a meeting that day with a reporter on some nature topic. Seeing me with my antennas, he was convinced I was a broadcast guy.

Meeting fellow hams

When fellow hams catch me with my antennas they will come over to identify themselves and exchange experiences. Most are stay-at-home-hams that find it hard to see the fun in going through all the work to play radio for a few hours. 
In PA I have met a dozen amateurs this way. Of course there are also fellow hams I organise to meet /P. Like Jakob OZ7AEI/P and Finn OZ3FI/P (sk) in OZ, Andrew M0YMA/P in PA and Auguste HB9TZA/P in HB0. On expedition in GJ I had the pleasure of meeting Nigel GJ7LJJ as well as Keith G8IXN who just happened to pass by. Incidentally we ran into Keith twice (small island..). Portable in DL one time DL1EBR came by to say hello.
It is always nice to get faces to the voices you have heard (many times) before.

And then there is the ham who works as a police officer, as I found out when a police van pulled over when I was activating a nature reserve in PA. The police officer started to ask some specific questions about what I was doing - which I found rather curious - only to "come out" and explain that he was a local ham radio operator. Not long afterwards I actually met him on the radio.

Sometimes there is only a link to the hobby: once a lady approached me to ask if I was a radio amateur to add that her late husband had been one.. and she really hated it (I did not have a witty return on that one). 

Twice I managed to sneak up to another ham radio operator working portable in my area. Once it was Swa ON5SWA working from PAFF-0019 (and SOTA) and the other was PD0RWL working from PAFF-0085 (and COTA-PA).

Sneaking up to PD0RWL with my loop - receiving an S9++++ report

Meeting other fellow humans

You meet all sorts of people out in the field. You recognise the different types over time. Some are curious but reluctant to approach you and others want to know all about it even when you are in the middle of a pile-up. 
Most are curious about what the fun is and sometimes I am able to transfer a bit of the magic of making radio contacts when I explain it to them enthusiastically (mostly they look wearily though). 

Once in a while you meet people that make a lasting memory. A few of the highlights:

Quite early in my "portable career" I was in a nature park when a group of bird spotters came over. I can't really understand the fun in what they were doing but they were serious about it - their whole outfit including massive binoculars screemed "serious spotter!". I tried to explain what I was doing but saw it did not click with them at all. I tried some other angles and then I mentally zoomed out and saw the absurdity of the setting with two species looking at each other as aliens.
Other alienating meetings are the ones with people that have their own reasons to be at the secluded places I usually end up at. There are the guys looking for guys. Slightly akward. So far I have not been approached (only scanned) so I think the elaborate setup of wires sort of gives away I am there for a different reason.
Another category is the "second love" pair - a man and woman arrive each in their own car. For a while they share one car and then drive off again (to unsuspecting "first loves" I guess).
Sometimes you get the feeling you have ended up in a play or a movie.

It happens that you scare people. Like the one time we were testing a lowband setup with the YNOMY team. We were working with high masts (including my 26m Spiderbeam pole) and lots and lots of wire in a small park when a local turned up in his Range Rover. Quite agitated (as in: nervous not aggressive) he asked us what we were doing. It is only afterwards that we understood that he was afraid something permanent would be installed. We missed the opportunity of pretending to be working for a telephone company installing a new tower (the poor man..).  

Then there is the odd encounter that actually is scary. So far I have had only one: I was in France in a nature park quite far from the civilised world. There was a small road through the park and looking at the map I had seen one tiny track just off that road to an open space next to a river (see photo below). I found the track and parked my car on it to find the open spot that clearly was visited more often judging by rubbish laying around and remnants of an open fire. I thought youths must be using that area. 
Remote place in France for a memorable FFF activity
Just when I had set everything up a car stopped behind mine on that narrow track. Out came a scruffy guy that looked completely bewildered. He asked me how I had found this spot - as if it was some sort of hidden place. It seemed he came there more often and was not particularly amused to find me there. He was uneasy, and when he learned I am from PA he started to refer to drugs - which I am not interested in so that line of conversation was rather short. I tried to ignore him and started playing radio. The notebook I was using for logging had (and still has) a broken screen. Not a problem for me as it is still usable but it attracted his attention. He walked to his car and came back with a notebook asking me if I was interested (so picture this: scruffy guy, hidden place, drugs, spare notebooks to share... not the best pal to share a remote spot with).

The next thing he did was even more cinematic: being slightly bored he started to fiddle with his notebook using his pocket knife. Okay.. so here we have the scruffy guy a few meters away with a large enough knife. Interesting.

This is the only time I was aware of and made sure that my hammer was within short reach.

My new friend did leave in the end but it was the least enjoyable radio-activity I have done so far.