Ray Wells vk2tv at exemail.com.au
Sat Feb 9 07:12:40 EST 2008

The Tait T500 series nmd-band radios (68-88MHz) readily covert to 6m by 
changing a handful of caps and adding a second slug to the tx VCO. 
They're synthesised, with diode matrix programming. I prepared the 
following about 6 or 7 years ago .....

Modifications to Tait T520 for 6m.
by Ray Wells VK2TV
Compiled long after the event from rough notes, memory and a look at the 


Fit an additional slug to the VCO coil. I salvaged one from an old 27MHz

Change C243 to 33pF (from 27pF).

L56 becomes 9T, 4mm dia. Enamelled wire as previously used
L60 becomes 9T, 4mm dia.          ditto
L62 becomes 2T, 4mm dia 22# TCW

Fit solder blobs to enable additional capacitors C266A and 266B.
Ditto for C 292.
Leave L86 shorted out by PCB track. (in LPF).


There doesn't appear to be an additional slug in the VCO but be aware that
one may be required. Injection is on the high side as it was for the 
original frequency range.

Change caps as listed. Value in brackets is old value.
C102    39      (6.8) strange jump in value but 39 works. Maybe the
has a wrong value at 6.8 as I suspect I would have only increased by one
two values. Too long ago to remember.

C103    22      (12)
C104    22      (18)
C108    3.3     (2.2)
C109    27      (22)
C110    3.3     (2.2)
C111    27      (22)
C112    100     (82)
C113    47      (39)
C114    3.3     (2.7)

My unit exhibited no strange behaviour during tune-up and readily produced
a clean 25 watts and 0.25uV. The test frequencies were 52.525 and 53.000.
No degradation in performance was observed over this range.

That's about it.

I've also modified the
AWA 25M - lots of work, and a spectrum analsyer is essential to get 
clean output. Big, bulky, old.
Communico 250E - not for the feint hearted. True FM, but the crystal 
can't be swung far enough to get 5khz deviation without extra circuitry. 
Not recommended. Physically small, old. Receiver has a 455khz second IF 
that uses an old AWA chip as the limiter/detector. These behaved badly 
in the presence of noise.
Midland? - was on 40MHz and the handbokk had cap and coil values for 
52MHz (There were A, B & C models covering from about 28 - 60 MHz.). 
Synthesised radio - requires special programming hardware. The EPROM is 
soldered into a daughter board. 50W radio with a great receiver.

Ray vk2tv

Jack Chomley wrote:

> I guess it may be a bit hard finding a singe band 6 metre radio? Using 
> an expensive multiband unit would blow the budget. I would put up 
> something IF I could find a radio, have plenty of TNCs :-)
> 73s
> Jack VK4JRC
> At 05:21 PM 8/02/2008, you wrote:
>> I had 6m FM (52.525, and later repeaters as well) in the mobile for 
>> 20 years and the car was used every day of the week. I wouldn't have 
>> notched up 50 contacts in 20 years. There was a hive of activity in 
>> the early days of 6m FM (around 1970?) but it dropped off fairly 
>> quickly. I ran the Sydney 6m AM net frequency of 53.866 mobile for a 
>> number of years prior to that net dying - not long after 6m FM became 
>> popular.
>> I used a 2m 5/8 whip with a diplexer to handle both bands on the same 
>> antenna - it worked as a slightly base-loaded 1/4 wave at 6m. 6m 
>> usually had more "legs" than 2m but it was knocked on the head more 
>> quickly by man made noise.
>> Essentially it will cost me nothing to install a 6m APRS frequency 
>> but I'd like it to hear something occasionally :-)
>> Ray vk2tv
>> Dion Bramich wrote:
>>> Id use it over 2m anyday mobile.
>>> On Tue, 05 Feb 2008 09:50:05 +1100, Richard Hoskin <vk3jfk at amsat.org>
>>> wrote:
>>>> Gday,
>>>> 53.100Mhz is in use in VK3 as a packet frequency. I know of at least
>>>> packet digipeaters here in VK3 that get some use.
>>>> If you want a six meter allocated frequency for APRS I can take it 
>>>> to the
>>>> WIA NTAC/FTAC.... I've just been cajoled onto being a member of the
>>>> National
>>>> Technical Advisory Committee for APRS and D-Star.
>>>> You will need to think about how much use 6mtr APRS will get first.
>>>> Cheers
>>>> Richard
>>>> VK3JFK
>>>>> -----Original Message-----
>>>>> From: ozaprs-bounces at aprs.net.au 
>>>>> [mailto:ozaprs-bounces at aprs.net.au] On
>>>>> Behalf Of Scott & Clare Evans
>>>>> Sent: Sunday, 3 February 2008 9:31 AM
>>>>> To: 'VK / ZL APRS Users'
>>>>> Subject: RE: [OZAPRS] 6M APRS
>>>>> In the outdated WIA list for packet radio 53.100 gets a mention for
>>>>> packet
>>>>> use maybe that could be a starting point!
>>>>> I was thinking of something similar here however no locals showed
>>>>> signs
>>>>> of interest so I didn't go any further with it!
>>>>> 73 de VK7HSE Scott Evans
>>>>> _______________________________________________
>>>>> Ozaprs mailing list
>>>>> Ozaprs at aprs.net.au
>>>>> http://aprs.net.au/mailman/listinfo/ozaprs
>>>> _______________________________________________
>>>> Ozaprs mailing list
>>>> Ozaprs at aprs.net.au
>>>> http://aprs.net.au/mailman/listinfo/ozaprs
>> _______________________________________________
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