Monday, June 10, 2019

QRO portable

Most of my QSOs I have made while out portable. At home I only have a simple antenna: a wire running from the attic window into the garden. Quite early on I found that to work interesting DX stations I had to have a better setup. At around the same time I discovered the WWFF and COTA/WCA programs. A portable journey had begun.

Why bother about the setup?
My radio time is rather limited. This is one of the reasons I want to make the most out of the trips I undertake. The other reason is that I like to give chasers all over the world a chance to collect references in the (worldwide) award programs I participate in as activator. 

Trying many antennas and setups I moved from simple wire antennas via a home made cobweb to the folding hexbeam. That one still is my favourite DX antenna. I use that one if I have the time and know there is enough room to set it up. For low bands I use verticals, a c-pole (40m), delta loop (40m) and dipoles (center and end fed). 
For ease of deployment I have lately started using a linked dipole in inverted V configuration for 20-80m. I am quite pleased with the performance and the ease of changing bands.

With antennas you are faced with the next challenge: height. I started out with an extended Spieth mast (14m but very thin top) and Spiderbeam 12m mast. Fine for end fed's (vertical / sloping) or high band dipoles but once you get to 40m and below you want more height. So I moved to 18m and later even 26m Spiderbeam masts. The 18m version is the one I take out by default. I added some features to make it easy to deploy on your own in the field.

Power - applied and transmitted 
Last but not least there is the question of power. I moved to LiPo and LiFePO4 batteries for my radio's years ago. The capacity / weight ratio is unbeatable. With LiPo's you can run 100w for hours with little added weight.
Moving towards the solar minimum I was looking for a bit more TX power. I started with a cheap RM Italy amp and then moved to the Ameritron ALS500m. It provides a max output of 400w - which is exactly what you are allowed in PA.
I purchased a lead acid battery of 145Ah to power that amp - with the idea that this would allow full day operations (like when I am on expedition with my team YNOMY). However this has two downsides: the battery is *very* heavy and it only supplies 12v or even less under load. At that voltage the amp - designed for 14Vdc - is putting out probably something like 250w.
For a while I looked into voltage booster solutions but I did not manage to build something that was practical and reliable at the same time.

By the end of 2018 LiPo's had become far less expensive than when I started buying them and I had collected a few already (sunk costs). So I decided to see if I could power the amp with LiPo's. The big advantages being that the amp would run at the designed 14v with far less battery weight.

In preparation of the YNOMY GJFF expedition I built three extra batteries from individual LiPo cells I bought in China. During the expedition we have run the amp for two days on LiPo's and the radios on LiFePO4's, using the 145Ah lead acid battery as recharging unit. This worked brilliantly.

HobbyKing 16Ah LiPo, DIY 20Ah LiPo and DIY 20Ah LiFePO4

The capacity required to run the amp for a given period of time depends on a number of variables, like the mode used and how much you transmit during that time. A couple of portable activities have learnt me that I need one LiPo battery (16/20Ah) per 90 minutes of SSB activity. 
In GJ we had four 16/20Ah LiPo's and when we drained one, we recharged it from the Lead acid battery (using a balanced charger). In the end we never drained all batteries as we had a recharged battery ready when we drained the next.

Note that with the Ameritron amp you can choose two approaches. The standard power leads consist of 4 wires (2+ and 2-). This means you can attach two LiPo's and run them in parallel. This is a way to extend your operation without needing to switch batteries in between. I chose a different approach. I left the original (longer) leads and added a short extra power lead (fused). The wires are just long enough to rest the battery on top of the amp.

[update 2020: I built a 5 cell in serial LiFePO4 battery for the amp]

Beware of low voltage
It is important to keep an eye on the voltage level of your batteries if you intend to use them more than once. You can buy battery alarms that monitor each cell in the battery. They will give off an alarm you cannot miss (think of fire alarms in your house) once a cell reaches a set minimum. I recommend you always have an alarm attached while using a LiPo / LiFePO4 battery.
For LiPo's in general 3.2v is used as a safe lower limit per cell. I think it is conservative and in this particular case too conservative as the current drain is high. This means that the cells will show a voltage dip from which they will bounce back a bit once you disconnect the battery. I therefore use 3v as the cell minimum for the LiPo's.
The LiFePO4 cells can go a lot lower. I set the alarm for 2.5v per cell - still quite conservative.

This setup is effective. Apart from direct experience (hardly scientific) I do once in a while get a chance to compare my results with other stations out in the field on the same day. As PAFF and COTA-PA coordinator I receive a lot of /P activity reports and logs. 99% of the time I was not out myself but the times I was, there was bound to be someone else out as well. In those cases the difference shows both in QSO rates as well as in distance covered.
This setup is also bulky. Last time I had to walk quite a distance in the sun with the radio, the 18m mast, the amp, batteries, antennas, chair, food and drink, and it was killing. Transport-wise there are still a few improvements I can and plan to make.

Lots of heavy stuff!

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