Prc-320

[QQVO6/40]

I am thinking of buying a PRC-320 packset radio. I have noticed a couple for sale in the UK. Granted they are rather expensive and will cost me around 140 Pounds to have one shipped out here to Australia.
I was wondering if they are any good as I wish to use it and not just look at it. I have an Amateur Radio licence so I am looking at using it on those HF bands as well as a back up set when I go bush so in an emergency I can contact the Royal Flying Doctor Service.
I was just wondering if there are any well known problems I should be aware of. I think they are over 20 years old so might just scrape into the old radio definition of this forum. Hihi.

Thanks in advance for any info.
Cheers.

Robert.

[G6Tanuki]

I've been using a PRC320 for quite a few years: they're really rather good for spot-frequency operation [you can often find me on 3.615MHz AM] but the "safe-cracker" frequency-synthesizer is not good for general purpose tuning-the-bands.

You're likely to get 'comments' about the audio: the PRC320 has a very aggressive speech-processor/VOGAD based on the Plessey SL600-series chipset - as a result it sounds a lot louder than most people would expect for a 30-watt-PEP radio! The downside is that many amateurs will find the sound of the audio to be rather odd.
With mine, I've had people say that on double-sideband, full-carrier AM it sounds more like 100 watts than 7.5 watts, but is rather 'rough'. That's just the VOGAD turning up the quiet syllables and mercilessly clamping the louder ones.

Things to watch out for: there's a known problem in the power-supply [module-5] - the 110V varicap rail for the synthesizer uses Tantalum capacitors which go leaky with age and the result is a few-KHz 'warble'. You can replace the Tantalum capacitors with 105-Centigrade-rated 160V electrolytics to cure this problem - if you catch it in time. Leave it too long, and the 120V inverter in module-5 cremates itself through trying to keep the stabilised rail at the right voltage despite the ever-increasing load from the leaky Tantalum capacitors.

If you want, I can provide you with a copy of the full PRC320 schematic/manual.

There's a good Yahoo group for PRC320-users too.

http://groups.yahoo.com/group/prc320/

My best contact using the PRC320 was UK-to-The-Falklands on 14MHz, using the standard 2.5-metre whip on the PRC320.

Also, if you need any guidance on connecting an Airlite-62 aviation headset to a PRC320 - I've done it, and it's really rather good.

--G6Tanuki.

[ex seismic]

I also have one, used mainly on 5MHz. I strongly advise joining the 320 group and going through the past messages. All the common problems are well documented.
As mentioned the HV rail problem seems the most common fault, you can't get at the relevant bits without major dis-assembly but a quick give away of impending doom is if you get a persistant unlocked tone at the high frequency end of each range.
You know of course from your reading that these are USB only, there is a simple enough kit to give you LSB. Your reading will also tell you about the quirky frequency selection by amateur standards (2 KHz offset) which is even quirkier with the LSB mod.
A bare radio is not useable, you need the 24v battery, audio gear, aerial and gooseneck to get something useable. A 12 or 24v charger (DCCU) is useful but at the end of the day the battery is just 20 NiCds so not difficult to charge. Two 12v SLA batteries are quite acceptable. Forget about the hand generator, this is for masochists only.
Don't let me put you off, these are great radios and punch way above their 30 watts. I've always had good audio reports from mine using the standard army audio gear. My best contact so far was probably northern Greece from the UK using the standard whip aerial.
Gordon
G7KNS
PS: The advertising blurb for the 320 calls it a lightweight backpack. It lies!

[trh01uk]

Originally Posted by ex seismic

PS: The advertising blurb for the 320 calls it a lightweight backpack. It lies!

I think they meant its "lightweight" compared to the stuff they hauled about previously!

Richard

[Sparky67]

I have used (and repaired...) and number of PRC320s over the years and would echo the comments made above. Having the internal ATU is a bonus too.

One tip if you do buy one Robert - always rotate the main band selector clockwise. Damage can occur to wafers in the turret and I've had a couple of radios which work if it's rotated clockwise / don't if it's rotated anti-clockwise! I have also had a couple of 320s where the fixed D-types on the front and rear chassis only just made contact and I ended up removing the outer case seal between the units to improve reliability.

Overall a great little radio for fixed-channel use, maybe not so good if you want to 'tune the bands'...

[QQVO6/40]

Hello all
Sorry for my late reply to all of your kind replies to my question. I have had a late slab of work thrown at me that has taken all of my attention for the past few days and threatens to disrupt my life for a couple of weeks. Please do not think that I have ignored your very informative replies.
The set up of the synthesiser as in single channels does not concern me as I have a list of set frequencies that I will be working on. I have a regular schedule with my son who is also a licenced amateur radio operator. I also have a Yaesu FT817 that I can use for just looking around the bands. The PRC-320 is a bit like an extra.
I have taken note of the various problems in your posts especially the one about the tantalums in the power supply to the synthesiser. It seems like the most destructive one mentioned so far.
I will keep up with the thread as things develop in the near future as in a months time I should be clear of my extra work.
I thank you all for helping me with his new project.

Cheers.

Robert.

[RobinBirch]

Originally Posted by trh01uk

I think they meant its "lightweight" compared to the stuff they hauled about previously!

Trust me, it is...

Robin

[QQVO6/40]

My radios have finally arrived. I now have a PRC-320/L and three PRC-351 radios along with heaps of other bits and pieces to play with. Masts,elevated antennas, wire dipoles and all sorts of little bits and bobs. I would not like to be in a full tactical position with all of this stuff set up and come under attack. Would take ages to gather up all of the little bits. Would need a corn sack to throw it all in and sort it out later.
I guess I have just started a long journey of exploration. All good fun though.
I love it!!!
Cheers, Robert.

[G6Tanuki]

I think the truth is thta in many combat situations the harrassed signallwe would just throw the longest length of wite he could over the nearest tree and hook it to the PRC320 then see if he was able to obtain a workable link.

I only ever saw PRC320s being used "in anger" in 3 setups.

1] Manpack, with the standard-issue 2.4-metre whip or sometimes a slightly-longer whip (about 3.5 metres) invariably 'liberated' from the USA equivalent of the 320.

2] With a dipole of some sort or an end-fed wire. The "end-fed-wire" people never bothered with the standard-issue PRC320 (a horror of spools and a real pain to wind up again when you get grass/brambles entangled in the 'legs' of the couterpoise). If they needed a better earth the usual thing was to use a bit of wire with a crocodile-clip one end and hook this to the nearest wire fence. I recall one station which hooked its ground-wire clip to the aluminium frame of the commercial 'polytunnels' they were using as cover, and everyone was astounded by their signal-strength.

3] As a driver for a vehicle-mounted 100-watt linear amplifier. The stupid thing about this setup being that the PRC320 still had to operate off its battery, it not being rated to handle a 24-volt vehicle supply on 'float' charge.

--G6Tanuki

[MaxIZ1GMJ]

And the first time that I have appeared on this forum, it is very interesting.
I have a PRC 320 full that I have not used very often, but it gave me a lot of satisfaction, I connected Spain, England, Greece, and W1AW in portable vertical antenna with 5.5 m. !
Now in reception on all bands goes up and down in frequency, power problem (CPU 5b)?
I had just replaced the electrolytic capacitors C8 and C6 with 160 V
and everything was OK for a few hours now 147 V output!!

Grazie molte

Max IZ1GMJ

[G6Tanuki]

Good to have another PRC320 user here.

The metal-cased-Tantalum electrolytic capacitors in the power-supply are a known failure point in the PRC320: they begin by going a bit leaky [so the voltage becomes unstable and the frequency of the synthesizer drifts] then they break down more and the driver-transistor that feeds the +130V step-up transformer works harder and harder to maintain the voltage until it fails.

There are also two similar Tantalum capacitors in the "Ramp generator" in the frequency-synthesizer module: as these get old they cause the same frequency-warbles and also cause the synthesizer to take forever to lock when you change frequency [lots of beeping in the headset].

[techiesteve]

An interesting thread. I've just taken delivery of a PRC-320, 2 batteries, 14V DCCU, headset, handset and rucksack. Also have the battery extension cable to cut up to connect to a mains 24V linear PSU.

Just out of interest, what value electrolytics replace the 1.7uF tantalums, 2.2uF?

[G6Tanuki]

1.7uF is a very wierd value. I used two Nichicon 1uF 160V acial capacitors in parallel [modern aluminium e-lytics are a lot smaller than the original tantalums so no problem physically fitting them!]

Genuine metal-cased Tantalums with NSN and lot-traceability were available but at a stupid price - 80 quid +VAT each!

[Jimmy0494]

Originally Posted by ex seismic

A bare radio is not useable, you need the 24v battery, audio gear, aerial and gooseneck to get something useable. A 12 or 24v charger (DCCU) is useful but at the end of the day the battery is just 20 NiCds so not difficult to charge. Two 12v SLA batteries are quite acceptable. Forget about the hand generator, this is for masochists only.

Was enquiring how to connect 2 SLA batteries up to the 320? Do I need a lead or cable as there are 2 connectors that battery slots into?

[G6Tanuki]

To run a remote battery (or a couple of SLAs) as power supply for a PRC320 you need a remote battery-lead:

The NATO stock-number of mine is 5995-99-620-2113

They crop up regularly on the auction-sites, or see here:

http://www.lrseries.com/shop/product...OWER-LEAD.html

for a non-Ebay supplier.

[Martin G7MRV]

Originally Posted by Jimmy0494

Was enquiring how to connect 2 SLA batteries up to the 320? Do I need a lead or cable as there are 2 connectors that battery slots into?

There are proper PRC-320 to 'open end' wire cables about for connecting to alternative supplies, but they seem very rare. The lead as shown in the link from G6Tanuki above is the 'cold weather' cable - Very useful to have as it means you can run the set on the bench and put the battery on the floor! But I would resist butchering it -

However, a 'dead' metal cased battery can usually be had for little more than the cost of shipping, and if the cells are stripped out, will hold (the 4Ah type) a couple of small 12v SLABs, or can be used to provide a connector block for external power (for this use a 1Ah unit, much smaller). This would then either clip on the radio or connect with the above cable.

Even good batteries are still quite cheap. The plastic ones are harder to rework though than the alloy cased ones

Although not as lightweight as a KX3, my PRC-320 went up Snowdon with me on sunday! I will admit though that that was with an alloy battery case stripped out and rebuilt with a 7S 4Ah LiPo! And i currently have a 7.9m vertical (the 5.5m mast and wire plus whip antenna) set up on my veg plot to play with the '320 when im gardening!