[VHFcontesting] Transmit Performance of the 222MHz Transverters Store Transverters (aka Ukranian Transverters)

[RT Clay]

Thanks for posting this. I have one of these 222 transverters and have used it for qrp portable. I bought just the bare board and assembled the rest myself. Some more comments:
1. Mine was also 13 KHz off. If you set the IF on frequency then the calling frequency comes out at about 222.087 
2. I drive mine from the transverter interface on a K3 (1 mW) with no attenuator. Even though this is less than the listed drive requirement on the docs that came with the transverter, I get about 7-8 W output. I never had any comments about a dirty signal, but I am in the middle of nowhere for VHF and have no close stations...I rarely work my own grid in a VHF contest.
TorN4OGW EM53



On Wed, Feb 15, 2017 at 8:50 AM, James Duffey <jamesduffey at comcast.net>
wrote:

> In preparation for the January ARRL VHF contest, W7QQ had two of the
> Transverters Store’s 222MHz transverters in his shack. These are the
> inexpensive, $125 fully assembled and packaged, less as boards,
> transverters available on eBay or from the manufacturer.
>
> As the reports of the transmit quality of these units are varied, some say
> they are OK, others say that the transmit quality is horrible, we decided
> to look at the transmit properties of the transverters. A short description
> of the results of those measurements are on the NM VHF Society Page:
>
> < http://www.nmvhf.org/technical.html >
>
> We found that one of the units had acceptable IMD performance and one unit
> was poor. This would explain the mixed reports. Upon further investigation,
> we found that the unit with poorer IMD performance had a lower final gate
> bias, 2.8V, than the good unit had at 3.1V. When the gate bias on the unit
> with the poor performance was increased to 3.1V, its performance
> substantially improved. The paper shows how the adjustment, which is
> straight forward, was done.
>
> Here are the IMD test results on the two units:
>
> Transverter 3rd order IMD Performance
> Power Out (watts)      Unit One        Unit Two (after bias adjustment)
> 7.5                    -12 dB                  -10 db
> 5                      -20 dB                  -18dB
> 2.5                    -28 dB                  -24 dB
>
> Two of the locals ran theses two units in the January ARRL contest and
> their signals sounded fine on the air.
>
> If you have one of these units, or are going to purchase one make sure
> that the final gate bias is set to 3.1Vdc or greater prior to putting it on
> the air. If you have a spectrum analyzer, you can look at the IMD while
> changing the final gate bias, if not, set it to 3.1Vdc according to the
> instructions in the paper. If it is already 3.1Vdc or greater, you are
> probably OK. There is probably room for further improvement as the internal
> settings for the drive potentiometer and the variable inductors on the two
> units differed. When we get the opportunity, we will look at this closer.
>
> If the power is kept below 5W, these should be acceptable on the air. If
> you are driving an amplifier, then you should probably keep the drive to
> 2.5W or less.
>
> The transverter boards for all of the VHF/UHF bands are similar, but we
> did not make measurements on transverters for other bands. I would expect
> the results to be similar, but not identical. If you have one of these
> units and measure the gate bias, I would like to know what it was before
> and after adjusting it.  - Duffey KK6MC
>
> --
> KK6MC
> James Duffey
> Cedar Crest NM
>
>
>
>
>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting at contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
_______________________________________________
VHFcontesting mailing list
VHFcontesting at contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting