[Amps] Henry 4 K-2 SWR

[TexasRF@aol.com]

The swr bridge certainly could be part of the problem. Another often  
overlooked cause of this problem is where the input and output coax  shield/center 
conductor is split apart to make connections to the relay and coax  connectors. 
If you measure the conductor diameter and spacing here and calculate  the zo 
of the short line section that is created, you will find the impedance  can 
exceed 200 ohms. The section is short but the high impedance can add a  
surprising amount of inductance to the circuit. Some or most relays will also  have the 
same effect. 
 
The effect can be compensated to a large degree by adding small capacitors,  
say 5 or 10 pF across the ends of the split coax. While this works, it may  
take some experimentation to find the optimum value capacitor. 
 
The infinite 6m vswr sounds suspect unless there is some kind of low pass  
filter in the circuit. The coax and relay effect mentioned above should not  
cause this on 6m.
 
Happy hunting!
 
73, K5GW
 
 
In a message dated 12/7/2005 7:47:20 P.M. Central Standard Time,  
w3ll at arrl.net writes:

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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