[CQ-Contest] Re: [UK-CONTEST] "IR" cans update

Clive Whelan clive at gw3njw.fsworld.co.uk
Mon Sep 10 19:33:46 EDT 2001

 Clive Whelan wrote:
> That's the good news, now the bad news. It seems they are 
> virtually useless for the purpose intended. What seems to be 
> happening is that the input stage of the base unit is being 
> overloaded even at quite low audio inputs.

Well I've started, so I'll finish ( sorry that's meaningful to 
UK readers only!).

A suggestion from Dave/G4BUO, which I hadn't thought of, was to 
hang a pair of conventional cans in parallel on the rx output, 
to "quieten down" the audio. Sadly this didn't work.

Having seen that a number of folk were using Philips units with 
success, I grabbed a pair of HV8350 at Argos for GBP39.99. I was 
encouraged that the spec. made great play of having input ALC to 
minimise overload. 

Imagine my horror, when the base unit looked virtually identical 
to the Thomson units, just a few cosmetic differences, and the 
identical plug top PSU was employed, being made in China.

However there *is* a big difference, although I have to say that 
it is not perfect by any standards. Now you must appreciate that 
I am a fussy *%$!)^ about audio. I still think that my old Shure 
444 is unsurpassed, but of course it's not a headset and it's 
50K not 600 ohms. Mind you I draw the line at low resistance 
speaker cables and gold plated connectors, but you get the 

The Philips unit still does overload, and the attack time on the 
input ALC, is not fast enough to prevent this ( have you ever 
heard  a Drake 2B attack the AGC, awesome stuff from what, 
1959?). My best guess is that the Sony device, and particularly 
the Senheiser would solve this problem entirely, but I am not 
looking to spend GBP100 on a pair of cordless cans.

There is now a real difference between the FT1000MP, which is 
virtually acceptable, and the TS930S which is still marginal. 
Overall on a scale of 1 to 10, I rate the Philips unit at 7, and 
the Thomson at 2/3. Thus if you're going for 863Mhz cans ( or 
whatever the equ. is in the U.S.) do ensure that they have input 
ALC. A further point is  that I think I was wrong aiming for a 
sensitivity of 105dB/mW or thereabouts. That would be good for a 
pair of conventional cans for use with the FT1000MP ( the Yaesu 
units are 102dB/mW) as I have found that good quality HiFi units 
of 96 or 98 dB/mW are unusable with the FT. However I now 
believe that 105B/mW or more is too sensitive for RF cans, and 
leads to excessive danger of input overload, although as 
highlighted earlier the top of range units may overcome this 
problem entirely.

The encouraging news is that my earlier purchase ( Thomson 
WHP540U for GBP 25 at Currys) is not a write off. The cans 
themselves work with the Philips base unit, since the same UHF 
channels are used, and the problem *is* with the base unit, not 
the cans themselves. So I have a spare pair of cans, and this 
will be necessary for contest operation, as the stated battery 
life of the Philips is only 15 hours. Thomson do not specify 
battery life, but I cannot imagine it is any better.

Although I am not 100% happy, the compromise is probably now 
acceptable, as I am fed up tripping over the long lead, and 
pulling a million interconnections off in the middle of a 
contest. Also as a *real* single operator, it will be great to 
go the kitchen ( and bathroom!) while keeping tabs on the band.

If anybody is flush enough to shell out for the Senheiser unit ( 
RF65 I think, GBP100 at Maplin) I will be interested to hear the 

Hope the above may save somebody frustration and unnecessary 



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