Friday, February 25, 2011

An FM/AM/SSB handheld for 10 and 12m

I love handheld radios. The "holy grail" for me is to make long distance contacts using a handheld radio with attached antenna. Ten metres is probably the best band to achieve this. Six metres might give stronger signals when conditions are right but it is open too rarely. Lower frequencies are open more often but a practical hand-held antenna is too short and inefficient for voice contacts using low power to be possible. You can put up a ground mounted vertical or hang a dipole in the trees but then it isn't portable.

Last year I got an Intek H-520 which I used on 10m FM but although I did make some nice contacts with it I was disappointed with the radio itself. It was very power-hungry for 6 NiMH AA cells to the extent that the radio would shut down when used on maximum power unless the batteries had just been charged up. There is another problem with 10m FM in general which is that there are not all that many channels. There is a lot of QRM when the band is open, you are competing with people running a lot more than 4W to a whip antenna and in the FM mode "capture effect" means the strongest signal wipes out all others. So when I saw that a multimode handheld including SSB and covering both the 10m and 12m amateur bands was available, I decided that this was the toy for the forthcoming summer months. SSB offers the chance for some exciting handheld contacts.

The Albrecht AE2990AFS is a multimode multi-standard CB handheld radio that is readily configurable for amateur band use. There are instructions on the web and even a YouTube video on how to do the modification but the supplier included a printed copy in the box. Briefly, you pull out the rubber PTT cover which reveals five contacts next to the PTT switch. Using a soldering iron and solder wick you remove a bridge between two contacts (preferably without touching the hot solder wick on the case and melting it like I did!) then you short out two other contacts while turning the radio on. You can then choose various channel options including three for hams: Code 0 (10m + 12m switching between them using the CH9 button), Code 1 (10m band only with home frequencies 29.300 and 29.600 selected using CH9) and Code 2 (12m band only.) I chose Code 0 to get the benefit of two amateur bands.

No batteries are supplied and no charger either. The lack of a charger is a bit annoying as the charger socket is a fairly small barrel type that isn't easily obtainable (even after you've guessed the dimensions.) The battery pack takes 9 NiMH AA cells and has contacts on the bottom. A drop-in charger is available as an optional extra. I will probably make one as I did for the old TH-205E. But first I have to establish what the charging voltage is. The box the radio came in suggests the charger/DC socket on the side of the battery pack takes 12V. You can certainly run the radio off that, but when it is switched off it draws no current. It looks as if you would have to crank the voltage up to about 18V to charge 2400mAH NiMH cells at 240mA, which would probably have dire consequences if you switched the radio on with the charger connected. But with the lack of propagation on 10 and 12 metres I probably have a few weeks to figure it out.

The antenna supplied is about 8 inches long. I checked it using my antenna analyzer and was pleased to find that it was resonant on 28.5MHz with quite a sharp SWR curve. However such a small antenna is probably little better than useless for making contacts over more than a few miles. I have a 45in telescopic 10m antenna and that is what I plan to use with this radio.

The Albrecht AE2990AFS is ready for the new European harmonized CB frequency allocation (which the UK wants to opt out of) so the output is rated at 4W on FM and 4W PEP on SSB. The actual power measured on 10m FM from this radio was only 2.13W. This is similar to what I found with the Intek H-520. With the Intek I was able to get inside, find the power adjuster and tweak it up to 4W. That's when I discovered why it had been set lower in the factory - the current draw at 4W is just too high for many AA rechargeables to sustain. Most CB users would never know their radio was giving less power than claimed because they have nothing to measure it with, so they would never complain. If it cut out whenever they press the PTT then they would. We hams complain that our radios are expensive but they are built to a higher standard than CB radios. You get what you pay for.

With its 9 cell battery pack the Albrecht doesn't need to draw so much current as the Intek for the same power. While it was on the bench power supply I measured the current draw on FM "high power" (2W) as 800mA. On the low power position which is meant to be 1W but was actually 0.51W the draw was 500mA. Unlike the Intek there is a "warranty is void if you remove this" sticker over the two halves of the case so I can't delve inside undetected. As I have heard of people who bought similar radios under other brand names which broke and had to be returned under warranty I don't want to void it, so I'll have to live with 2W output, at least until next year.

On SSB the modulation out of the box was almost nonexistent. This is dependent on the mic gain setting, which can be adjusted from the front panel. After increasing it the SSB modulation was much improved and although I don't have a peak reading meter the average level gave me to believe I was getting 4W PEP.

The audio on SSB sounded clean but if you increase the mic gain in order to get reasonable talk power there is noticeable frequency modulation on the signal. I am guessing that the battery voltage sags a bit on speech peaks and this pulls the local oscillator. I had read about this issue in some forums discussing the other incarnations of this radio and someone stated that in the Albrecht versions this problem had been fixed. It appears this may not be the case. I doubt that the fault would make the audio unreadable but I would expect to receive comments about it.

I recorded a number of audio samples at different mic gain settings for comparison. You can hear the FM increase on voice peaks as the mic gain increases.
When configured for ham band use the radio displays frequency as you would expect. The display has an attractive blue backlight. Tuning is by up/down buttons at the side. There is an annoying beep at every button press, but this can easily be silenced. The standard tuning step is 10kHz which is a bit large for convenient band scanning. You can change the step size for fast or slow tuning - the steps are 100kHz, 10kHz and 500Hz. The 500Hz step size is still a bit large for satisfactory SSB tuning. There is a clarifier control but it works on receive only. So some people you call will complain you are off frequency.

There are five memory channels which store frequency and mode, so you can switch quickly between FM and SSB calling frequencies for example. You can select a shift or offset of up to 990kHz for repeater use. There is also a CTCSS tone for repeater access, but the manual implies it is a fixed 88.5Hz tone which (apparently) is used by 10m repeaters in the USA. This is straight from the manual - I can't vouch for it.

With the lack of any propagation on 10 or 12 metres I obviously haven't had a chance make any contacts with the radio or evaluate the receiver sensitivity. The RF gain and squelch sensitivity can also be adjusted from the front panel in the same way as the mic gain. There is even a roger beep!

So there you have it. The below-specification power and FM-y SSB audio are fairly major faults, all things considered. But the Albrecht AE2990AFS is the only true handheld SSB-capable radio for any amateur band currently available. If that's what you want, it's your only option.
Post a Comment