[amsat-bb] Moxon on top a Baofeng UV-5R for 70cm experiment

[Richard Tejera]

Pavel, yes, the Baofengs are going to defense on 70 cm, it's what you get for $30.00. 

The good news is Fox 1 is U/V, so the De 
Sense shouldn't be a problem. Or at least less of one. 

73
Rick
K7TEJ

On March 16, 2015, at 19:50, Pavel Milanes Costa <co7wt at frcuba.co.cu> wrote:

Yes, that's the tool for the job.

That was my starting point, then with mmana and nec I made some 
adjustments on the design, cosmetics adjustments...

The final result is few mm more or less against the generated by moxgen...

A few minutes ago I tested the antenna on the SO-50 pass... 56 degrees 
pass here, among others I heard K8YSE, UE1FG/MM, K?8KW, K4FEG.

RX: Success, strong and clear signal till LOS...
TX: a real failure, STRONG desense, I think it's problem of the "cheap" 
RX radio...

Setup here: RX Baofeng UV-5R with the moxon on top, almost ZERO coax 
length, TX Feidaxing FD 268A 5/1 W with coax to a Jpole with almost 10m 
of RG-213 Coax... (+ 1m of soft RG-58 pitgail from the radio to the RG-213)

The Jpole is 5 meters away and about 2 meters above my head.

No matter if I use 1 or 5 Watts, once I press PTT the baofeng goes deaf 
and only noise is heard with my scrambled voice on it (this voice is not 
from the sat)

This can be the 3rd harmonic of 2m, but it's normal to get this behavior 
with the baofeng or other radios?

What can I do for improve/solve this situation?

A low pass filter (LPF) for 2m right on the output of the TX radio?

The Baofeng is the only option here for RX on 70cm... this is driving me 
crazy...

73

El 16/03/15 a las 20:37, Richard Tejera escribió:
> Pavel,
>
> Here is a link to a program as m called MOXGEN. It will calculate the dimensions for a moxon given the frequency &wire size. Once done it'll generate an EZ-NEC model for the antenna.
>
> The model should give you a good idea of the gain, beamwidth & front to back
>
> http://www.moxonantennaproject.com/design.htm
>
> I'd be interested I what it tells you.
>
> 73
> Rick
> K7TEJ
>
>
>
> On March 16, 2015, at 17:05, Pavel Milanes Costa <co7wt at frcuba.co.cu> wrote:
>
> Hi to all.
>
> Yesterday I was evaluating the construction of a small antenna for
> portable use on top of the Baofeng UV-5R... at the end I finished with
> two choices CJU vs moxon for 70cm handheld
>
> After some modeling I choose the moxon over the CJU because:
> - Smaller
> - Less wire
> - Less weight
> - Less stress for the connector
> - Just ~0.6 dB down vs the CJU
> - By far better F/B ratio
>
> After completion of the first "prototype"...
>
> I successfully heard the CW beacon of Jugnu, CO-57, CO-58, PRISM and others.
>
> The fire test will be tonight on SO-50, I know now I will copy ok, but
> the challenge is eliminate the desense of having two yaguis on a cross boom.
>
> I will test the moxon handheld on RX (UHF) and a Jpole for the 2m uplink
> with 5W of a handheld.
>
> I have not measured the SWR of the moxon, but with the simulation the
> measures are not "that critical" for getting a less than 1:2 of SWR over
> the entire 70cm band (1:3 bandwidth is about 16 Mhz)
>
> The moxon "experiment" is just ~25 cm width and ~15 cm height (may be
> smaller also, the minimal height is ~10cm + connector) over the Baofeng
> UV-5R, there is no much stress on the connector.
>
> I used a SMA to BNC adapter (the kind with a rim to fit tight to the
> radio body) and then a clamp on BNC (male) with a bronze tube as coaxial
> shield/boom of the antenna.
>
> Wish me luck with the desense problem...
>
> 73
>