M175 High SWR

[2315 Robert]

Robert, I am glad you are back in business. I have one question though, how are you taking standing wave ratio measurements without a meter that reads reflect? Do you have access to a facility or a friend with gear?!

As you can tell I am no good at typing what I am thinking or doing. So let me give it a go. Yes I have several SWR meters of different brands and price ranges. So I take an average of them all. The numbers I just posted were all the same on all meters. As far as the 54m I used a HP 8920A I just picked up from action this last week on the antenna(they are only good for 60w direct input) using the spectrum analyzer. And my completely unconventional way of checking things is with a piece of wire wrapped around the coax(thief) with leads to an ebay 8 digit frequency counter powered by my power supply. If the numbers hold steady on AM or SSB with a 1 khz tone applied all is well. Another completely unconventional way is to add a fan to the box if it stops so should you. Just wanted a meter with reflected(a number warning sign) and swr for the mobile. That is where I have had things changed and caused problems.

 

[LeapFrog]

As you can tell I am no good at typing what I am thinking or doing. So let me give it a go. Yes I have several SWR meters of different brands and price ranges. So I take an average of them all. The numbers I just posted were all the same on all meters. As far as the 54m I used a HP 8920A I just picked up from action this last week on the antenna(they are only good for 60w direct input) using the spectrum analyzer. And my completely unconventional way of checking things is with a piece of wire wrapped around the coax(thief) with leads to an ebay 8 digit frequency counter powered by my power supply. If the numbers hold steady on AM or SSB with a 1 khz tone applied all is well. Another completely unconventional way is to add a fan to the box if it stops so should you. Just wanted a meter with reflected(a number warning sign) and swr for the mobile. That is where I have had things changed and caused problems.

Very respectable, kudos for going DIY and learning some things along the way!

I was using a simple watt meter in the beginning, one day I notice the power going off the scale, that reference point helped me notice something was way off; (coax was not screwed on)

Indeed a warning system is a good thing, I like the fan idea!

 

[Tallman]

As you can tell I am no good at typing what I am thinking or doing. So let me give it a go. Yes I have several SWR meters of different brands and price ranges. So I take an average of them all. The numbers I just posted were all the same on all meters. As far as the 54m I used a HP 8920A I just picked up from action this last week on the antenna(they are only good for 60w direct input) using the spectrum analyzer. And my completely unconventional way of checking things is with a piece of wire wrapped around the coax(thief) with leads to an ebay 8 digit frequency counter powered by my power supply. If the numbers hold steady on AM or SSB with a 1 khz tone applied all is well. Another completely unconventional way is to add a fan to the box if it stops so should you. Just wanted a meter with reflected(a number warning sign) and swr for the mobile. That is where I have had things changed and caused problems.

Does it look like this?

 

[2315 Robert]

Does it look like this?

Affirm. Mine is probably 5 wraps of 14ga.

 

[2315 Robert]

I would try adding a negative-feedback network to each transistor. A 100-ohm 2 Watt resistor in series with a 0.1uf capacitor will frequently calm down a twitchy amplifier built with high-gain transistors like MRF455. The series-pair of parts goes from each transistor collector to the base on the same transistor.

This will change the amplifier's input impedance, tends to lower it. Check the input-side SWR with a meter between the radio and the amplifier while it's keyed and producing power. There is usually a capacitor in parallel with the input transformer's primary. Trimming the value of this cap will frequently fix the problem and get the input-side SWR back below 2 to 1. A trimmer cap can be wired in place of the fixed cap, and used to zero in on the optimum capacitance value. You can then remove it, measure the value and install a fixed part close to that value, or just leave the trimmer where it is.

This method has worked for us numerous times.

73

nomadradio will have to fix an car radio amplifier for an employee tommorrow. I will be using the .01 cap and 100ohm on a 400 boomer tomorrow. Will put that thing in proper working order. Internal on board is almost useless.

 

[nomadradio]

Umm, a 0.1uf cap tends to work better than a .01uf part.

Better than nothing, but I have had disappointing results with a .01uf cap.

73

 

[2315 Robert]

Umm, a 0.1uf cap tends to work better than a .01uf part.

Better than nothing, but I have had disappointing results with a .01uf cap.

73

miss type.0.1 will be used.

 

[2315 Robert]

Umm, a 0.1uf cap tends to work better than a .01uf part.

Better than nothing, but I have had disappointing results with a .01uf cap.

73

Nomadradio I think I taming a Shrew. I know that this is not a clean box(actually I used to run a Palomar 400 HD(not HD low dead key and swing that was available from radios in that era) in the mobile many a year ago. It was a very good mobile and one day it was stolen(stole my 1983 toyota pickup) at a Rite Aid and parked that night in front of Police station. This things is crazy. If I thought there was a small amount of influence off the onboard trimmer that is gone. As soon as I did.1 cap to 100ohm the onboard went no service. Makes my MegaWatts 50 amp supply rattle(like a small washer on a tiny screw is loose on during modulation). The Shrew is Katherina and she lives in this box resists care or recommendations.