[MRCA] Retransmit Project Phase 2

[W2HX]

Breck, et. al,

I started doing some more research on the issue of interference and hazards to the radios in this set up. Here are a few random things I have read.
1. PRC-138 receiver input protection is up to 70 Vrms.  I do not know if the power amp and antenna coupler provide any further protection to the receiver. They may or may not, but we have a minimum protection figure of 70vrms.  I am not experienced enough to know whether it is possible for the 50W sincgars system to induce 70 Vrms onto the antenna of the HF radio, but my gut tells me no.  I hope to separate the HF and VHF antennas by 100-200 feet and I think that distance should be safe.

2. I have not been able to find specification on the receiver input protection for the RT-1439/PRC-119. Similarly, I don't know whether using the 50W power amp in front of the RT provides any additional protection. Anyone out there know? I do plan to  use a low pass filter on the output of the HF radio so that any harmonics that may venture up into the 50 MHz range would be filtered and not cause desense or reception in the nearby VHF receiver. However, it is still TBD whether 125W 100-200 feet near the VHF receiver antenna could be detrimental

3. I located an army training document that, among other topics, has a section on "Special Siting Considerations" If the reflector will indulge me, here is an interesting excerpt:

<QUOTE>
The modern C^2 system uses multiple colocated radios to provide an effective communications system. The potential exists for a number of different radio sets or configurations to interfere with each other. This chapter provides procedures to minimize detrimental effects of colocated  systems operating in the same frequency ranges. The interference problem is broken down into three categories:

IHFR to IHFR
Sincgars to Sincgars
Sincgars to MSRT/RAU [not sure what this is]

[an now an interesting paragraph]
IHFR effects on Sincgars or MSRT should be minimal since IHFR operates in a frequency band separate from the other two systems. The procedures discussed here are near-term measures to ensure successful use of all three systems"
</QUOTE>

So this document seems to downplay problems associated with colocation of HF and VHF systems.  We shall see, of course!

If anyone has any real world experience in this area, please share your experience.

 
73 Eugene W2HX
 

-----Original Message-----
From: B Smith [mailto:smithab11 at comcast.net] 
Sent: Tuesday, September 11, 2012 6:29 PM
To: W2HX; mrca at mailman.qth.net
Subject: Re: [MRCA] Retransmit Project Phase 2

Beware of running high power and having two separate antenna systems, an easy way to blow a front end unless the receiver is  protected.  Some systems have built in protection - - - I have an HF  set on the bench that has front end protection up to 50 volts but I prefer not to test it. 
:-)

Z

--------------------------------------------------
From: "W2HX" <w2hx at w2hx.com>
Sent: Tuesday, September 11, 2012 5:47 PM
To: <mrca at mailman.qth.net>
Subject: [MRCA] Retransmit Project Phase 2

> Hi all,
>
> The other day I posted my limited success in getting a 20W HF radio
> (PRC-138) interfaced for retransmit with the low power (4W?) PRC-119.  
> As I move through the phases of getting a whole system up and running, 
> the next step was to get the PRC-119 set up in the vehicle mount using 
> the RF amp for high power output. Although I've owned the VRC mounts 
> and amp for a while, I've never had the chance to test it out. Well 
> today I did, and voila! Everything worked like a charm.
>
> If you are interested, please see the video I made detailing the 
> testing for power out using the RT-1439, AM-7238/39, an AS-3900 
> antenna standing on a tripod.
> Next steps is to get the PRC-138 connected to the 125W power amp, 
> RF-382A antenna coupler and interface the two.
>
> This is where things will get interesting, running two high power 
> radios with antennas in the same backyard! It will be interesting to 
> see what interference arises and what the practical realities are of 
> such a set up in a small backyard.
>
> Enjoy.
>
> http://www.w2hx.com/x/PRC-119/VRC-90-Power-Test/
>
> (hint, watch the videos in numeric order)
>
>
> 73 Eugene W2HX
>
>
>
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