F/S RACAL ACOUSTIC RA6000 TALON PTT
Group. I have for sale 3 of the above items for sale, these are new old stock asking ?33 each. plus pstge
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Jeff?
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G8XXI
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Folks,
see my previous reply to this thread.?? That was correct because the set uses a linear PA - not a hi-level modulated PA.
73s
Richard
G7RVI
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On Mon, Mar 24, 2025 at 12:23 PM, gm0uhc wrote:
Anyway ... everything is working fine. Press the PTT in AM mode and you get 20W of carrier ... apply an appropriate audio signal, the ammeter on the PSU drops from 3.5A to 2.5A and the power drops to 8W.?
Thats not quite right , the residual carrier should be lower than peak-out , as the pa is linear, its presented with a generated spectrum, by allowing carrier leak through , the carrier side band levels are determined by the? drive levels , no mixing should take place in the? PA, at a guess, the? set will? be generating a lot of splatter ??
?
its possible to have a? mod index greater than '1' , but, the? negative swing will? not pass ''zero'' on peaks the? side band/carrier ration will? exceed normal proportions on peaks, this give higher ' apparent modulation level'?
?
something? is 'wrong with the? drive levels ... or the? pa linearity ?
?
73-Graham
g0nbd?
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Re: Synchronous AM on the RA6790
On Fri, Feb 28, 2025 at 09:16 PM, Peter E wrote:
does not show any evidence of this happening
That's simply? because there is no phase locked carrier insertion oscillator in Am mode? , the detector carrier is derived from the clipped off-air signal. if the carrier fades out, then Thers nothing to re-inject , as the? tune passes over the signal, the carrier / side band relationship ,remains unaffected.?
?
The RA1771&2 , 1778 have carrier locked AFC , again if the carrier drops then the? Afc holds the? last good lock frequency?
the afc enters at the? 34 M osc to alter set tune, not linked to the? detector[s]?
?
This and ssb/isb enables better recovery of? AM , but, thats using the? internal phase locked CIO and the? filters to
present the? detector with usb/lsb signal ,?
?
Anything on from this, need to add DSP , something like RTL dongle in direct sample mode and sdr-sharp or other ,
looking at the 455K IF out [or 1.4 MHz ra 1778] , various 'locked'? detector modes are then available ...?
?
73 Graham
g0nbd?
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?
?
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Ian, Yes, I also cut my amateur teeth on various VHF PMR radios, with sometimes quite fiddly adjustments to get the modulation right, and adding to the power output, with an increase in PA current on speech peaks, rather then a reduction. ? Not something I have really pondered since, especially as the effect at the received end is not noticeable usually. ?? With regard to PA failures on the 931 family, on the two radios I've replaced PA's on, they were operating into an antenna via the roller coaster internal ATU, on 80m, into quite short antennas and at a guess the PA's were exposed to a higher RF voltage when tuning (or the antenna changing impedance), due to the quite high Q. ? ? By comparison, the same PA devices when used in a PRC-320, seem a lot more rugged, although the internal ATU on the 320 is lower Q, with ferrite pot-core inductors that are lossier overall. ? A PRC-320 with an ALC/APC fault can produce around 100-110W of RF, although it obviously gets very warm, quickly, so the devices seem to have a degree of head room. ? I'm glad that your 931 is now producing full power again, however it modulates! ? 73 Al G8LIT
?
------ Original Message ------
From: Ian@...
To: [email protected]
Sent: Monday, March 24th 2025, 12:23
Subject: Re: [RacalRadio] TRA-931
? Many thanks to Alan, G8LIT For his enlightening reply ... Downwards Modulation. ? Wow! It must be at least 45 years since I last heard that term. Being first licenced as GM8LWR back in 1976, when most of us operated ex-PMR AM mobiles, we were very familiar with Downwards Modulation, characterised by the ammeters on our PSUs dipping, rather than peaking on speech peaks. I suppose that since then, we have been accustomed to AM and SSB being the product of the same Balanced Mixer. ? The 931 is an interesting beast in that the TX side actually bears a close resemblance to the MA79 Drive Unit. The 1.4MHz in each case is the 14th harmonic of a 100KHz signal. Both use a balanced mixer ... and even the following filters are configured in a similar way, with the AM (or DSB, in the MA79) filter being somewhat similar. Given that the MA79 generates AM and DSB from a very simple balanced modulator, I do find it odd that in the 931, the modulator is deliberately unbalanced in order to generate AM in this form. I understand it, I just don't know that I understand the reasoning. ? Anyway ... everything is working fine. Press the PTT in AM mode and you get 20W of carrier ... apply an appropriate audio signal, the ammeter on the PSU drops from 3.5A to 2.5A and the power drops to 8W.? ? Thanks again, Ian, GM0UHC www.chavfreezone.me.uk?
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Ian,
its due to the inter-relationship between CW and AM.??? The 20W
you mention will be CW only.??? On SSB you will get 20W PEP.??? On
AM you will also get 20W PEP.
But AM is not normally measured as PEP.?? Its measured in steady
carrier power.??? And to get 20W PEP of AM, the carrier power has
to be 1/4 of the peak power.? Hence 5W of AM.
Its a point skated over by many people when rating power
outputs!???
Amateur radio limits demonstrated the same logic.??? It used to
150W of DC input power to your PA.??? That would generate about
100W of carrier power, but 400W PEP.??? Hence when SSB arrived the
power limit became 400W PEP.....
best regards
Richard
G7RVI
You wrote
? TRA-931
From: gm0uhc
Date: Sun, 23 Mar 2025 09:29:23 PDT
Hi,
I currently have on my bench a Racal Syncal 30 aka TRA931. I'm
currently involved in looking into alternative PA transistors
since good 2N5070s are nearly impossible to source these days.
I currently have a pair of 'experimental' transistors in place
and the set is happily generating 20W on all frequencies with a
very slight drop (about 2W below 2MHz). What is a bit alarming is
that the set will happily deliver 20W (in the High position) even
when AM is selected. Oddly, although the manual specifically
states that the o/p is nominally 5W on AM (and understandably
too), there is no mention in the circuit description of how this
reduction in output power is achieved.
?
Looking at the wiring associated with the Mode Switch, it looks
like the Mute pin (66) on the synthesiser might have something to
do with it, but poking around in that area has proven
inconclusive.
?
Can anyone shed some light on this?
?
Regards,
?
Ian, GM0UHC
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Many thanks to Alan, G8LIT
For his enlightening reply ... Downwards Modulation.
?
Wow! It must be at least 45 years since I last heard that term. Being first licenced as GM8LWR back in 1976, when most of us operated ex-PMR AM mobiles, we were very familiar with Downwards Modulation, characterised by the ammeters on our PSUs dipping, rather than peaking on speech peaks. I suppose that since then, we have been accustomed to AM and SSB being the product of the same Balanced Mixer.
?
The 931 is an interesting beast in that the TX side actually bears a close resemblance to the MA79 Drive Unit. The 1.4MHz in each case is the 14th harmonic of a 100KHz signal. Both use a balanced mixer ... and even the following filters are configured in a similar way, with the AM (or DSB, in the MA79) filter being somewhat similar. Given that the MA79 generates AM and DSB from a very simple balanced modulator, I do find it odd that in the 931, the modulator is deliberately unbalanced in order to generate AM in this form. I understand it, I just don't know that I understand the reasoning.
?
Anyway ... everything is working fine. Press the PTT in AM mode and you get 20W of carrier ... apply an appropriate audio signal, the ammeter on the PSU drops from 3.5A to 2.5A and the power drops to 8W.?
?
Thanks again,
Ian, GM0UHC
www.chavfreezone.me.uk?
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Running in AM linear mode you will need to drop the carrier to 1/4 peak power to allow headroom for positive modulation peaks. Frank WA1GFZ
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Ian,
My experience of repairing a 931, with failed PA¡¯s was to try a pair of PA devices from a working PRC-320 back panel. ?They just about produced 20W, as the drive was slightly down from the 2N3866¡¯s compared to that used in the 320, and the bias
current was slightly higher with the 931 bias circuit.
I had the same experience as you with AM, that it produced full carrier, and in my case downward mod, which was clean, and sounded good on air, and via a remote SDR.?
As it was a repair for a friend, and they were happy with it, that was then end of the experiment, and it soldiered on for many years after that until sold.
I don¡¯t know how closely the respective PA¡¯s were tested and matched by Racal and Plessey, but I changed them as a pair, so was probably lucky!
73
Al
G8LIT
toggle quoted message
Show quoted text
Hi,
I currently have on my bench a Racal Syncal 30 aka TRA931. I'm currently involved in looking into alternative PA transistors since good 2N5070s are nearly impossible to source these days.
I currently have a pair of 'experimental' transistors in place and the set is happily generating 20W on all frequencies with a very slight drop (about 2W below 2MHz). What is a bit alarming is that the set will happily deliver 20W (in the High position)
even when AM is selected. Oddly, although the manual specifically states that the o/p is nominally 5W on AM (and understandably too), there is no mention in the circuit description of how this reduction in output power is achieved.
?
Looking at the wiring associated with the Mode Switch, it looks like the Mute pin (66) on the synthesiser might have something to do with it, but poking around in that area has proven inconclusive.
?
Can anyone shed some light on this?
?
Regards,
?
Ian, GM0UHC
?
|
Hi,
I currently have on my bench a Racal Syncal 30 aka TRA931. I'm currently involved in looking into alternative PA transistors since good 2N5070s are nearly impossible to source these days.
I currently have a pair of 'experimental' transistors in place and the set is happily generating 20W on all frequencies with a very slight drop (about 2W below 2MHz). What is a bit alarming is that the set will happily deliver 20W (in the High position) even when AM is selected. Oddly, although the manual specifically states that the o/p is nominally 5W on AM (and understandably too), there is no mention in the circuit description of how this reduction in output power is achieved.
?
Looking at the wiring associated with the Mode Switch, it looks like the Mute pin (66) on the synthesiser might have something to do with it, but poking around in that area has proven inconclusive.
?
Can anyone shed some light on this?
?
Regards,
?
Ian, GM0UHC
?
|
Re: MA4091 automatic filter unit
On Fri, Mar 21, 2025 at 03:45 PM, Tone wrote:
Is that in any way similar to the MA-4015? I have one of those,
Tone G7TXU
I don't think so. The one I have in mind had a number of filters (six?) switched by crystal can relays controlled by a data cable from the radio.
?
It was over 40 years ago ...
--
Mike G8GYW
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Re: MA4091 automatic filter unit
Is that in any way similar to the MA-4015? I have one of those,
Tone G7TXU
On 21/03/2025 14:19, Mike via groups.io
wrote:
toggle quoted message
Show quoted text
Does anyone have one of these, or pictures of the inner
workings?
?
I pretty certain I worked on the design of this unit but
can't find any information online to jog my memory.
?
--
Mike G8GYW
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MA4091 automatic filter unit
Does anyone have one of these, or pictures of the inner workings?
?
I pretty certain I worked on the design of this unit but can't find any information online to jog my memory.
?
--
Mike G8GYW
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Many many thanks Dave, that's fantastic news. I can now put it to work rather than just have it sitting around looking pretty. Maybe it will work nicely with crossband on 6 and 4 metres.
Please excuse the typo, I did indeed mean the RACAL TRA-4072 PASSBAND VHF FILTER.
Indeed I measure 5.9 ¦¸ passthrough resistance on all six ranges.
If you have any literature on this unit you can share Dave, that would be excellent,? I can find next to nothing online. Best regards, Tony G7TXU  
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?
Hi Tony
I take it the unit is an MA4072 being the filter unit. It is designed to go between the 967 and the 970.
?
8 watts maximum is the spec. There is also a DC path to operate the MA972 antenna matching unit.
?
Regards?
Dave g1jwg
?
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Hi chaps, I've just received one of these 6 band VHF filters today. It physically bolts onto the TA970H VHF RF amp and also the MA989/E frame.
What I need to know is whether it can handle the TX power of a 3W TRA967 transceiver? on its way to a TRA970 VHF RF amplifier.
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Re: Greetings and RA.1217
On this link you can find my notes related to the RA.1217, if you are interested.
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Had someone the same problem with the coil cores?
(the file is 120 Mb)
?
?
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Re: Greetings and RA.1217
Good Morning to All,
?
thanks for your letters.
?
I continued my work: now I have two receivers which both at least comply with the overall requirement at 3.5 MHz.
But I am giving up. All the problems I found were due to the broken cores. I could replace some of them from the donor and discovered that they are not only fragile: many are already broken. Removing them is not easy but I could with pain succeed (in one case, also the new one broke immediately). Tuning up the whole receiver is not realistic, there are tens of cores in the 1217. I never had a similar experience before, I also checked the devices with a Geiger counter...
?
I will write down a few notes of the done work and then I will post, should they be useful for others.
?
Thanks anyway.
?
Gianni
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FS: two Racal MATEL digital field telephones
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Re: Greetings and RA.1217
I have three receivers from a friend. I would like to restore at least one (for him) and possibly one for me.
- Receiver #1: someone recapped its PSU and rewired it. Its PSU cannot be any longer detached.
- Receiver #2: it blew fuses, I recapped it and now it switches on.
- Receiver #3: is fairly incomplete and I use it as a donor for parts.
CORES: the worst problem I found until now is that many CORES of the RF/IF transformers became ultra-fragile. It is enough to just touch them, and they break, remaining jammed. I could not find a better way than drilling them out and get a new one from the donor.
IF MODULES ¨C I recapped the electrolytic capacitors. #1 was not working in the BFO section. I discovered that someone intentionally cut a trace. Now it works and complies with the minimum requirement (82 mV output, minimum is 80). #2 works but must be tuned (jammed cores).
Now receiver #1 complies with ¡°Overall Sensitivity Test¡± (volume 2 page 3-9). I cannot test it practically because here I have an incredibly strong electrical noise and no antenna.
Receiver #2 does not comply with the overall test (20 mV IF output instead of 60 mV).
The suggestion I am asking for is: I would not like to follow all the adjustment process for the receiver #2. What strategy do you suggest?
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Mike
Tone