Dynon COM weak and broken

[rvator51]

My Dynon COM is being reported as weak, broken, missing every other word by pilots in the air and unicoms on the ground. Its a new installation with RG-400 cable and a new VHF antenna from Delta Pop.

I hooked a SWR meter to it today and got the following readings.
118.000 Mhz 8.2 w power, -1.15 reflected power, 2.2 SWR

127.000 Mhz 2.6 w power -.66 w reflected power, 3.0 SWR

136.000 Nhz 5.5 w power 1.22 w reflected power, and 2.8SWR

Is it normal to have such a big power drop midway through the frequency range? Is there anything these numbers say about possible causes for weak transmissions or area to troubleshoot?

I am using a new Zulu 2 headset and also tried with a DC headset.

 

[CGameProgrammer]

I don't have a SWR meter but my symptoms are exactly the same as his and no solution has yet been posted to my thread...

 

[n456ts]

I'm not a radio guy, but those aren't good numbers to me. It looks like a cable or antenna issue? Your SWR is high - maxed in one case and above the spec of the antenna for the other two tests. The antenna mfg states a ground plane of "46 inch in diameter for the VHF antennas". Do you have a correct ground plane?

 

[GalinHdz]

Sounds like the antenna is not making a good solid ground connection. Check for dirt, corrosion or something like that where the antenna connects to the airframe (assuming it is an aluminum airplane).

 

[jnmeade]

Are the reports from frequencies all across the band? If so, are they consistent or are some frequencies better than others? Do you hear everyone OK on all frequencies? Have you tried using a different antenna on the ground, maybe connecting the radio to a correct homemade dipole to isolate the antenna? Tried swapping the antenna cable out?

 

[rvator51]

Here are the power out by frequency:
118.000  8.7
119.000 7.8
120.000 5.8
121.000 4.4
122.000 3.3
123.000 2.6
124.000 2.4
125.000 2.5
126.000 2.4
127.000 2.5
128.000 3.0
129.000 3.7
130.000 4.9
131.000 6.5
132.000 9.1
133.000 11
134.000 10.8
136.000 5.5

I hear everyone ok on all frequencies
Tower hears me ok on 120.1. Unicom and other airplanes can't make me out on 122.8 and 123.0
I am creating a ground dipole to omorrow and trying this antenna and a different antenna.
I cut off the ends of existing cable and put new ends on with no change.

 

[rvator51]

Sounds like the antenna is not making a good solid ground connection. Check for dirt, corrosion or something like that where the antenna connects to the airframe (assuming it is an aluminum airplane).

It's a new antenna with new RG400 cable on new aluminum airframe bottom of Vans RV-6a.  The new Delta Pop antenna is composite on base. 
Looks like only grounding takes place through the mounting screws.

 

[jakej]

Whenever I install antennas I always use a star washer under the head of the screws (only need to do that on one) & the nut as they bite into the metal to give good 'bonding'.

 

[rvator51]

Good idea. I have star washers under both nuts. I swapped antennas and made a new cable and tried it today. Becoming convinced radio is the problem.

 

[Raymo]

Also interested in your outcome as my Dynon radio is being reported by tower on 126.25 as having the same issues. Other frequencies seem to be fine.

rvator, which SWR box are you using? I've been looking at getting one...

 

[rvator51]

Search for Redot or Tenq SWR meter on Amazon.  I also just ordered a Frequency counter to verify the frequency output.

 

[rvator51]

Dynon is sending me a replacement radio to use while mine is being inspected/repaired. Great Dynon support as usual!