[Amps] Henry 4 K-2 SWR

[R.Measures]

On Dec 7, 2005, at 7:05 PM, Mike Schatzberg wrote:

> Hello Bud:
>
> It is possible that there may be some contamination on the contacts of 
> the
> T/R relay, and you might try cleaning them if they are open frame.  If 
> they
> are vacuum relays, there isn't much you could do except to replace 
> them.
> Don't forget to inspect the associated coaxial cables or just replace 
> them
> with new cabling.
>
> If there is no problem with the relay or relays and associated coaxial
> cables, the problem may be caused by the inductive reactances in the 
> T-R
> relays and the coaxial cabling.

At its characteristic Z, coax has zero reactnace, so my guess is that 
Henry Radio did not compensate for the XL in the output relay by adding 
a parallel C of c. 30pF.
>
> It is not unusual for the SWR to raise to as high as 2:1 on ten meters
> because of this inductive reactance.  This inductive reactance can be
> canceled by adding some capacitance from the common terminal of the 
> output
> relay to ground.  You might try adding 10 pf to ground, and re-measure 
> the
> SWR.  If the SWR decreases, add additional parallel capacitance, and 
> recheck
> the SWR again.  A couple of 10 pf 1 KV NPO caps may do the trick 
> nicely, at
> least up to 10 meters.
>
> It is possible that operation on 6 meter frequencies thru the amp 
> by-pass
> was not envisioned by the designers.  You may have to make further 
> circuit
> modifications to permit that possibility.  You should be able to assure
> operation thru 10 meters in any event.
>
> 73 and Happy Dxing,
>
> Mike
> WB2AJI
> ----- Original Message -----
> From: "Bud Governale" <w3ll at arrl.net>
> To: <amps at contesting.com>
> Sent: Wednesday, December 07, 2005 8:46 PM
> Subject: [Amps] Henry 4 K-2 SWR
>
>
>> When passing thru the Henry 4 K-2 amp, with the amp turned off,  the
> exciter sees an SWR of between 1.1 to 2.0 depending
>> on the band the exciter is set on (75M thru 10M). The SWR is higher 
>> at the
> higher frequencies. The SWR is infinitely
>> high on 6M.
>>
>> If connected directly to the antenna(s), the exciter sees 1.1 SWR on 
>> all
> bands. I'm using a SteppIR antenna whose
>> elements can be tuned to present a flat impedance at any frequency 
>> between
> 40M and 6M.
>>
>> With the amp turned on, the exciter sees an SWR of 1.1 on all bands 
>> (75M
> to 10M).
>>
>> My question is why does the amp introduce a higher SWR in bypass and 
>> not
> allow a 6M signal to pass thru without
>> introducing an infinitely high SWR?
>>
>> In the off position, the signal passes thru an input bypass relay and 
>> then
> to an internal SWR bridge at the output side
>> of the amp and then to the antenna.
>>
>> With the amp turned on, the signal passes thru the input relay and to 
>> the
> appropriate band input impedance matching
>> module. This explains the 1.1 SWR on all bands with the amp turned on.
>>
>> The only components in the path, with the amp turned off, is the 
>> bypass
> relay and the SWR bridge - all internal to the
>> amp. Can these be causing the exciter to see the higher SWR and 
>> infinite
> 6M SWR? Is the internal SWR bridge the culprit?
>> Any ideas?
>>
>> 73,
>>
>> Bud W3LL
>> w3ll at arrl.net
>>
>>
>>
>>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org